Gwang Min Gu

The cortical activation pattern by a rehabilitation robotic hand: a functional NIRS study

Introduction: Clarification of the relationship between external stimuli and brain response has been an important topic in neuroscience and brain rehabilitation. In the current study, using functional near infrared spectroscopy (fNIRS), we attempted to investigate cortical activation patterns generated during execution of a rehabilitation robotic hand. Methods: Ten normal subjects were recruited for this study. Passive movements of the right fingers were performed using a rehabilitation robotic hand at a frequency of 0.5 Hz. We measured values of oxy-hemoglobin (HbO), deoxy-hemoglobin (HbR) and total-hemoglobin (HbT) in five regions of interest: the primary sensory-motor cortex (SM1), hand somatotopy of the contralateral SM1, supplementary motor area (SMA), premotor cortex (PMC), and prefrontal cortex (PFC). Results: HbO and HbT values indicated significant activation in the left SM1, left SMA, left PMC, and left PFC during execution of the rehabilitation robotic hand (uncorrected, p < 0.01). By contrast, HbR value indicated significant activation only in the hand somatotopic area of the left SM1 (uncorrected, p < 0.01). Conclusions: Our results appear to indicate that execution of the rehabilitation robotic hand could induce cortical activation.

Design of a novel tremor suppression device using a linear delta manipulator for micromanipulation

In this paper, the design of a high precision device using a Linear Delta manipulator was proposed to compensate for the tremor signal in three translational directions. A Linear Delta manipulator is a suitable tremor suppression device due to the simple structure and high stiffness with the vertical direction in the application of micro manipulation such as microsurgery and cell manipulation. In order to implement the mechanism of the Linear Delta manipulator to the device, three voice coil motors and three linear encoders with high resolution were used. The flexure mechanism was applied to the device to avoid the friction effect of the small ball joint. Finally, the experiments for the validation of the proposed device were performed as follows: (1) position control in each axis for accuracy, and (2) sine wave tracking (500 μm, 12Hz) for bandwidth of the system.

Robotics for Healthcare

Since the first industrial robot was introduced in the 1960s, robotic technologies have contributed to enhance the physical limits of human workers in terms of repeatability, safety, durability, and accuracy in many industrial factories including those of the automobile, consumer electronics and shipbuilding industries. In the 21st century, robots are expected to be further applied in healthcare, which requires procedures that are objective, repetitive, robust and safe for users. Fueled by the rapid improvements of medical imaging and mechatronics technologies, healthcare robots have been rapidly adopted in almost every stage of the medical procedure by surgeons and physical therapists. In this chapter, we describe applications and the state of the art of healthcare robotics developed in the last decade. We focus on research and clinical activities that have followed successful demonstrations of early pioneering robots such as daVinci telesurgical robots and LOKOMAT training robots. First, we categorize major areas of healthcare robotics. Second, we discuss robotics for surgical operating rooms. Third, we review rehabilitation and assistive technologies. Finally, we summarize challenges and limitations of biomedical robotics as assistive tools for medical personnel.

Development of a one-body optical torque sensor for rehabilitation robotic systems

This paper proposes a one-body optical torque sensor. The proposed sensor has advantages of anti-slip and low cost due to the simple one-body structure. Simulations for stress and strains analysis are accurately performed. To demonstrate the performance of proposed design, experiments were also carried out to compare it with a commercial force/torque sensor (Mini45, ATI).

Flexible insole ground reaction force measurement shoes for jumping and running

There are only a few insole ground reaction force (GRF) measurement systems for running and jumping because the capacity and durability of the system were not guaranteed to measure the heavy load on the foot. We propose insole-type measurement system that can measure up to 900N to assure the capacity of GRF during running and jumping. The proposed system was implemented using a sensor-embedded flexible shoe including four custom optoelectronic based force sensors with high reliability. In order to evaluate the performance of the proposed sensor, static loading and unloading tests were performed to compare the hysteresis with the force sensitive resistors (FSR) which are widely used in insole-type system. During test, FSR and the proposed force sensor were loaded to the reference force sensor simultaneously; the hysteresis error of the proposed system (4.8%) was better than that of FSR (23.54%). By utilizing these custom force sensors, the proposed system was manufactured and evaluated for walking, running at 8km/h and withstanding high jump experiments with the 6-axis force plate based on NRMSE (Normalized Root Mean Square Error). The results were 14.68± 4.75% for long period walking, 10.9± 6.5% for running, and 14.72± 4.44% for jumping. From these results, the proposed system helps to measure GRFs in real-time for various human movement.

A hand-held micro surgical device for contact force regulation against involuntary movements.

Involuntary movements such as heart beating in surgical environment and surgeons tremor disturb a micro surgical manipulation and cause a risk of patient wound. Although the delicate operation is performed by a skilled surgeon, the sensitivity of the surgeon is limited to quantify the range of safe contact forces. In this paper, we developed a compact hand-held surgical device to maintain a required contact force to maintain a required contact force using a custom force sensor and a linear delta mechanism. The custom optical force sensor measured the contact force of the device tip and the linear delta mechanism compensated undesired forces to maintain a consistent contact force. The proposed device is consisted of force sensing unit and actuating unit. The device was improved from our previous Linear Delta mechanism based prototype in terms of size, weight, and force sensing capability. The developed device was validated by investigation of contact force accuracy in a fixed condition and a hand-held condition. In hand-held condition, the visual feedback of the current contact force was provided, and the performance of the contact force regulation was investigated by comparing the root mean square (RMS) contact force errors and standard deviation in with and without control cases. The fluctuation (less than 50 mN) of the force regulation control of the device showed the feasibility of the device for the use in delicate operations.Involuntary movements such as heart beating in surgical environment and surgeons tremor disturb a micro surgical manipulation and cause a risk of patient wound. Although the delicate operation is performed by a skilled surgeon, the sensitivity of the surgeon is limited to quantify the range of safe contact forces. In this paper, we developed a compact hand-held surgical device to maintain a required contact force to maintain a required contact force using a custom force sensor and a linear delta mechanism. The custom optical force sensor measured the contact force of the device tip and the linear delta mechanism compensated undesired forces to maintain a consistent contact force. The proposed device is consisted of force sensing unit and actuating unit. The device was improved from our previous Linear Delta mechanism based prototype in terms of size, weight, and force sensing capability. The developed device was validated by investigation of contact force accuracy in a fixed condition and a hand-held condition. In hand-held condition, the visual feedback of the current contact force was provided, and the performance of the contact force regulation was investigated by comparing the root mean square (RMS) contact force errors and standard deviation in with and without control cases. The fluctuation (less than 50 mN) of the force regulation control of the device showed the feasibility of the device for the use in delicate operations.

SMAFO: Stiffness modulated Ankle Foot Orthosis for a patient with foot drop

Weight and power consumption of variable stiffness actuation mechanism are critical for its implementation in a portable assistive device combined with an actuator, gearhead, elastic element, and batteries. Therefore, we present a portable stiffness modulation mechanism for an Ankle Foot Orthosis (AFO) utilizing pneumatic stiffness. The mechanism consists of two units: a driving unit that controls an air pump and an AFO unit that performs free motion and stiffness modulation functions. The actuation from the driving unit to the AFO unit via pneumatic hose makes the effective weight of the device light compared to the direct driven device at the ankle joint. We derived a mathematical model of the stiffness modulation to determine the pressure required. In order to control the required stiffness according to the gait phases, a threshold-based gait phase detection algorithm was implemented, employing ground reaction force sensor signals from heel and forefoot. The effectiveness of the proposed AFO was validated by the experiments in a patient with foot drop, performing walking with and without AFO actuation.

Foot pronation monitoring using wireless biaxial force sensing system

Measurements of multi-axial Ground Reaction Force (GRF) can provides quite useful information for monitoring abnormalities of gait during Activities in Daily Living (ADL). Measuring multi-axial GRF using ambulatory GRF sensing systems is difficult due to the height of sensor and the number of sensors used. Therefore, we developed a wireless GRF sensing system having the low height (12 mm) and the capability of sensing simultaneously lateral and vertical GRF using only four optical sensors. The proposed biaxial force sensor showed the low interference rate (less than 0.1 %) and excellent repeatability (0.6 %). We extracted the lateral and vertical GRFs via Bluetooth communication during normal and pronated/supinated walking and presented a three dimensional vector diagram employing center of pressure and GRFs to provide visualization of the ratio between the lateral and vertical GRFs according to the amount of foot pronation. In healthy subjects, the lateral forces were observed less than 10 % of their bodyweights, while large lateral forces were observed in over pronated/supinated walking up to 20 %.

Investigation of a tolerable time delay in SEMG-based elbow assistive device

Surface electromyography (SEMG) signal has been widely used to detect the intention of the user in assistive device, because the onset time of the SEMG signal is observed before the muscle force development. The time between the onset of SEMG activity and the development of force is defined as electromechanical delay (EMD). Owing to the existence of EMD, an SEMG-driven approach has advantage of early detection of the intention compared to other approaches, especially to a force sensor-based approach. However, few studies have been done on the investigation of the timing of the assistive force considering EMD. This study suggests the proper timing of the assistive force for better performance by analyzing the onset of muscle force development. Simultaneous measurements of four channels of SEMG, interaction torque, control input corresponding to the assistive torque, and joint angle allowed the investigation of the quantitative relation between the onset of SEMG and timing of the assistive torque. The timing of the assistive force was manipulated by varying the amount of artificial time delay. The experiments were carried out for 3 subjects, who were informed to complete 4 repetitive elbow flexion/extension motions as quickly as possible, with the help of the assistive device. Task completion time was examined as a measure of the performance of the assistance, and cross-correlation analysis was conducted. We observed that the reaching time and level of SEMG activation were reduced when the delay was consistent with the EMD of the user.

Upper-limb assistive device for the elderly at home

We present an upper-limb assistive device for the elderly at home. In previous researches, the passive systems were manually adjusted to support arm movement with holding different weights of objects, and the active systems equipped with multiple actuators and sensors were too complex and expensive to use in hospitals and rehabilitation clinics as well as homes. If the assist for the activities of daily livings (ADLs) is to be delivered not just in the clinic, but also in the home, the system can facilitate the independence of the elderly in ADL. The presented assistive device consists of one active joint for the vertical motion and three passive joints for the horizontal motions. In order to reduce the required motor torque induced from the weights of the user arm and links of the device, a gravity compensation mechanism using parallel links with two springs was implemented. The vertical assistive force is provided according to the users intention that is extracted from the surface electromyography (sEMG) and interaction force. The effectiveness of the assistive force was validated by comparing the sEMG signals for the movements with and without the assistance.